1. Field of the Invention
The present invention relates to the general field of infrared detectors working at ambient temperature and notably to detectors comprising a pyroelectrical material.
There currently exist infrared detectors that can be used to make, in particular, infrared imagers. These detectors work in ambient conditions without any cooling system. To work properly, the sensitive material in the detector is heated by the infrared radiation. The rise in temperature may lead to the appearance of charges (for the pyroelectric detector function), variations in dielectric constant (the dielectric bolometer function) and variations in resistance (the resistive bolometer function). The major problem with these detectors is that of confining the heat within the sensitive material, by the prevention, to the maximum degree, of losses by diffusion within the substrate comprising the circuits for reading the response of the sensitive material.
2. Description of the Prior Art
Different approaches for insulating the sensitive material have already been envisaged. For example, the sensitive element may be attached to the reading circuit by means of conductive epoxy resin pads.
Metallized polyimide pads (U.S. Pat. No. 4,740,700 by Hughes) could also be used as shown in FIG. 1. The method used in both cases is a hybrid method that is difficult or even impossible to implement in batch production. This means that the matrices of detectors are made one by one.
Another approach proposes the use, as a sensitive layer, of pyroelectrical conductors with low conductivity that can be adapted to a less sophisticated level of thermal insulation (Patent FR 89 08799). It is notably proposed to use, for example, a layer of a polyimide type standard dielectric layer, between the silicon reading circuit and the pyroelectric polymer. Thus it becomes possible to reduce losses by diffusion in the sensitive layer, with a microelectronics type of batch production mode, but the performance characteristics and sensitivities of these detectors make it necessary again to consider other approaches in order to further improve the thermal insulation.